Massive perturbations to atmospheric sulfur in the aftermath of the Chicxulub impact

Abstract

SignificanceSulfur isotopes confirm a key role for atmospheric sulfur gases in climatic cooling, mass extinction, and the demise of dinosaurs and other global biota after the Chicxulub bolide impact at the Cretaceous-Paleogene boundary. The sulfur isotope anomalies are confined to beds containing ejecta and, in the immediately overlying sediments, are temporally unrelated to known episodes of volcanism that also bracket this event, further addressing the controversial role of the Deccan Traps in the extinction.

Keywords: K-Pg extinction; mass extinction; mass-independent fractionation; sulfur cycle; sulfur isotopes.

Fig. 1.

Sulfur isotope data (δ³⁴S and Δ³³S) from chromium-reducible sulfur. The study interval reported here is relative to a composite depth scale, reflecting the stratigraphy of three sections exposed along DMC, which are separated by ∼200 m. Biostratigraphic and lithologic designations are modified from Yancey and Liu (28) and Hansen (24) (see SI Appendix for details on stratigraphic correlations and new biostratigraphic data). The small, vertical dashed lines reflect the composite depth interval of samples taken from the condensed DMC “downstream” section. Basal Conglomerate Bed (BCB), Spherulitic Conglomerate Bed (SCB), Hummocky-Sandstone Unit (HSU) and Calcareous Clayey Horizon (CCH) are K-Pg event deposit units defined by Yancey and Liu (28).

Fig. 2.

Cross-plots of δ³⁴S and Δ³³S data. The upper shaded region in A shows the results of a sulfur cycle box model [modified from (34)] that produces minor deviations in Δ³³S resulting from mass conservation effects (MCE). MCE occur during microbial sulfur cycling, here modeled at four specific fractionation factors (colored lines) for microbial sulfate reduction, using the δ³⁴S and Δ³³S of Maastrichtian seawater sulfate as an initial condition (31). Colored dashed lines further indicate the results of a mixing model between Maastrichtian seawater sulfate isotope values and these generated sulfides, showing how mixing processes could produce negative deviations in Δ³³S, albeit smaller than those we measure here. B shows the results of a second mixing model that combines one sulfur end member with an S-MIF signature approximating volcanically derived sulfates with a second sulfur end member with a sulfur MDF signature similar to preevent pyrite. This model, which most closely reproduces our data, shows the mean ± 1σ of sulfur products produced by varying the S-MIF end member from +1 to −1‰ in Δ³³S using a Monte Carlo method.

Fig. 3.

Orthogonal data regression (17) showing Δ³⁶S/Δ³³S slopes and 3σ CIs of the regression (shaded region) for Maastrichtian and Paleogene samples (A) and for samples with ejecta materials within the impact event bed deposits and the sample from the basal Paleogene that overlies the event bed deposits (B).